Voice operated repeater circuit



July 12, 1932. B G BJORNSON 13566592 VOICE OPERATED REPEATER CIRCUITFiled June "I, 1950 2 Sheets-Sheet 1 I r- R) 1 Illt I FIG //v l/ENTO/PB. G. BJc'iRA/so/v ATTORNEY Patented July 12, 1932 UNITED STAT S :eroa ve. BJoBNsoN, or nnw Yong, 1p

PATEN T OFFICE essrenoa To Barr. rnnernonn .pnppnnr roams; mcoaroamanyoanew roan, 1v. an, A coax-cannon" cr ne-w Yoniz" v0. 9 or-naarn errarea.QJ B I Application filed June 7, 1930. Serial ll'o, 4 59,652.

The present invention relates .to voice operated transmission circuits,particularly to two-way transmission circuits containingoppositelydirected repeaters which are condix5 ltloned for .operation one at atime.

An object of the invention is to improve the operation of voice operatedsystems, particularly as regards speed of operation, sensitivity andfreedom from false operation.

Voice operated circuits areknown in .the art employing an eastwardand awestward repeater which are rendered operative one at a time by speechwaves. arriving at the repeater point for transmission through therepeater. To condition the respectiveare- .peaters for operation, someof the voice energy is rectified to produce a'voltage which .is used tochange the normal bias on one or both of the respective .repeaterssothat one -,g .repeater remains blocked Whiletheother is rendered incondition :to repeat.

In order to prevent clipping, that is, loss of any of the speech eitherat' the beginning or at the end of a word, it is necessary that gsvtherepeaterbeplaced in operating condition sufliciently soon to transmitthe initial portion ofthe speech and also that the repeater have asufficient hangover time to accommodate the end portion of a word'orsyllable.

application of the speech to the repeater so as to permit longer timein-which to condition the repeater, it is obvious thatthe voiceconswitching and release operations and secure I minimum of clipping. .7I

While reference-is made'throughout to 'voiceoperated circuits andtotwo-way transmission, it will be understoodthat the invention'in itsbroader aspects 'isapplicab-le to other types a of transmission thanspeech transmissions and is 1 also applicable, to .one-

way as well asltwosway. transmission. .a

"The inventionwill be better understood from the following detaileddescription with positive operation of the repeaters with a concerned inimproving comprises the voice Where delay circuits are not used to delayand-amplifier iYZ. The .amplifier'rectifier is reference to theaccompanying drawings 7 Sho ng n F g: 1 n chem ti dia ram two-wayrepeater circuit in accordance with the inventiQIl and in'Figs. ,2 and,3, curves illustrative of theoperation of the circuit of 1g. 1. r

he g n ral l you o th cirQut 9i E g- 1 is in accordance with prior, artpractice and will not require detailed description. 'l he portionof thesystem which the invention is op a c u sh w in h cent a PQItiQI of thefigure.

The westand east linesL and L re speo tive y ar a P v d W h hybrid co ld b a cing network N omm n n the art. The west to east repeater circuitis connected between the bridged conductors 10 of line L and the circuit11 connected to the series winding of thezhybrid coil of line L Forconvenience of descriptiomthis. ,vvest to east repeater path will bereferred to ajs thetransmitting branch. The east to West transmissionpath I is con: nected between circuit 12 bridged across the hybridcoilof line L and circuit 13 leading to l n .Lw- F r c venien e o desc iptiqn this eas o W pa w l b fe ine-. dton-$ the receiving branch.

'Thetransmitting branch contains thevacnum tube-relay circuit 1 4together with such amplifier stages as may be desired, indicatedgenerally at 15. Similarly, the receiving branch comprises the vacuum tul relay 11;.6

generally indicated at 18.;andthe receiving 1 disabler or protectorcircuit is indicatedgenerally at-l H 1 ia th p i r a speec Ware arr vingat. '10 the ransmi ing br nch, pass in ape-13 into, the amplifierdetector circuit.- 181 where y are, ra at d n st ady d re c r- .rentvoltage WhiQh is used to make. the n'ormally inoperative vacuum, tube relay ,l lopera iv and t disa e, th norm l y, p ratiy c v ng el y circitrl Th isl don y V 1 e u g-t no m nega v 1 biasro r ay 14: and pply gnegativ bias o. hegrid or. r lay l vThu th amp fie spee h. Waves inthe,outputofamplifier'l5, in caseof 3111- no balance of the network andhybrid coil of line L will not find their way from circuit 12 throughrelay circuit 16 to amplifier 17 and set up singing around the repeaterloop, because relay 16 is effectively blocked.

Similarly, received waves in the circuit 12 are transmittedthrough thenormally operative relay circuit 16 and amplifier 17 and are impressedon the west line L A portion of thewaves in the output of'amplifier17 isrectified at 19 and applied to the amplifier detector circuit 18 todisable this circuit so that it is not operated by energy that may bepresent in circuit 10 dueeither to noise or lack of balance of thehybrid coil of line Lwp v i The improvements provided by the presentinvention will-now be described. As stated above, these areconcerned-with the design of the amplifier detector circuit18 and thedisabler circuit 19.

The amplifier detector circuit 18 comprises an initial push-pull stage20 followed by an amplifier stage 21 and a rectifier stage 22. There isalso a bias reversing stage 23 cooperating' with'the'rectifier 22 asabove described to reduce the normal bias of relay 14.

Initial push-pull stage 20 has a normal negative bias impressed fromsource 2% slightly in excess of a value sufiicient to reduce the spacecurrent substantially to zero. It was seen in the foregoing descriptionof the operation of the circuit as a whole that received speech wavesoperate through the disabler 19 to impress an additional negative biason push-pull stage 20. This bias is applied across resistance 25. If thepush-pull stage 20 had normal space current flowing through the tubes,theapplication of the bias to resistance 25 from the disabler wouldfirst have to reduce the space current to zero, after which a furtherincrease in the negative bias would effect'the blocking of the push-pullcircuit 20 against false-operation. Such sudden reduction of the spacecurrent to zero wouldbe likely to cause the transmission of an impulsethrough the rest of the amplifier detector circuit 18 such as mightinterfere with the operation of the vacuum tube relays 14 and 16. Theuse of push-pull tubes in stage 20 would tend to minimize that efiect'es'peciallyif perfect balance could be obtained. However, by making thenegative "bias from source 24: such as to reduce the space that theapplication of additional bias to recurrent in stage 20 to zero, it willbe clear sistance 25 as described makes no change whatever in the outputof stage 20andtherefore precludes the possibility of a disturbingimpulse from this cause in circuit 18.

mplifier stage 21 (which may be one of several amplifier stages,depending upon the amount of gain required in any case) contains a highresistance 26 in the gridvcircu-it, theefi'ectof which isto cause stage21 to rent curve 1 reams That is,-it does not respond to input levelsbelow a certain minimumbut transmits cur rent nly when the minimum levelis ex ceeded.

The effect of the foregoing provisions in the amplifier'detector circuitis readily seen by reference to the graphs of Fig. 2. The zero line atthe left indicates the condition with no input from circuit 10. As theinput level increases from zero there is a marginal range of nooperation represented'by the distance between the zero line and thevertical line B. This marginal region is determined by the amount of.normal negative bias in stage 20. With further .increase of input levelstage 20 begins to transmit current in accordance with thecharacteristic I On account of resistance 26 in stage 21 this stagereaches saturation very quickly after the initial input voltage isapplied. This is indicated by the grid current curve I The rectifiercurrent is shown by the curve I which shows a slight marginal operationwith respect to I This is secured by the use of negative bias voltage27. By the use of suificient amplification between stage20 and rectifier22 the current curve I of the rectifier ismadevery steep and tube 22 iscaused to reach saturation when the input level has-exceeded by a fewdecibels, the minimum operate level. As. indicated by the labeled pointson curve I the complete operation point isreached atan'inputlevelof lessthan 1 db. and preferably 0.5 db. above the initial operate point. ,Byinitial operate point is meant the pointat whichthe circuit 18 isbiased, that is, the level of input at which the amplifier detectorbegins to transmit current. r

If there were no marginal, operation in the stage 20 orin the rectifierstage 22, it will .haps double the rectifier current, and so forth.

However, by the use of. a suitable marginal operation I together withsufficient amplification, the rectifier current might be multiplied by,say, 10 for only a small .percentage increase in' input level. The biasin. stages 20 and 22 plus the use of sufficient amplification make for avery steeply rising rectifier cur- It is important from the formhangoveri and uniform. release. operation, that the rectifiercurrentcurve I reach a maximum shortly. after the full-operate level.This action is secured-by use of the grid resistance 26'making stage 21saturate quickly.

standpoint of 'unigradually reducing level as the end of a word 7 orsentence is approached, would gradually reduce the amplifier detectorvoltage with likelihood that the final portion of the speech would belost by clipping. In accordance with the invention, however, therectifier current is kept up at its full saturation level for inputlevels only slightly greater than the initial operate level. Graduallyweakening input speech therefore tends to maintain the same bias voltageon the system as do stronger sounds. This action makes the releaseoperation practically uniform for sounds of weak as well as strongending.

In Fig. 3 curves are given showing the variations in gain with time andalso with input level of the vacuum tube relay circuits 14 and 16. Thesecurves are self-explanatory. It. will be observed that the systempossesses the following desirable operating characteristics: V

1. The receiver is blocked before the transmitter gets into fulloperation.

. 2. The receiver gain plus the transmitter gain is less than normalgain at all times during the switching or transition period.

3. The change from normal receiving to transmitting is completed for asmall change in input lever (AL=O.5 db-.).

4. The operate time is very fast, of the order of 0.001 second, forsuddenly applied tones, greater than about 2 db. above initial operatepoint.

5. The release time issuflicient to give slight hangover to preventterminal clipping.

The disabler circuit 19 of Fig. 1 comprises an initial amplifier stage30 and a push-pull rectifier stage 31. The negative bias source 32 andthe grid resistance 33 give the circuit 19 suitable marginal andsaturation characteristics of the general nature indicated above inconnection with the amplifier detector circuit 18. The use of a doublewave rectifier 31 avoids delayed or wrongly timed operation due to phaseshift. The use of a very small condenser 34 across the resistance 25 ofstage 20 gives a fast build-up time for the disabling voltage. All ofthese factors cooperate to give fast operation and uniform operate andrelease conditions. By adjust-' ing the characteristic of the full wavedisabler rectifier 31 in relation to the characteristic of the push-pulltubes of stage 20 practically a straight line relation can be obtainedbetween the disabler input level and the limit of suppression of thetransmitting vacuum tube relay circuit 14. This is desirable since thelimiting action of relay circuit 14 must increase to give greaterprotection against false operation as the waves in circuit 10 increase.The fast action secured by this circuit is necessary to prevent amomentary impulse being sent through the transmitting control circuitwhere no receiving delay is used, as in the case of the circuit of Fig.1.

What is claimed is:

r 1. In a voice operated circuit, a circuit for producing a directcurrent voltage from speech energy, comprising a-rectifier preceded byan amplifier, and means to make the operation of said rectifier andamplifier marginal, said amplifier reaching substantial saturation atthe input level corresponding to initial operation of said rectifier.

2. In a voice operated circuit, a vacuum tube rectifier normally biasedagainst operation, a three-element space discharge amplifier feedinginto said rectifier, means to im press speech waves on said amplifier,said amplifier having a high input resistance causing the amplifier toreach substantial sat uration at the input level at which the rectifierbegins to operate. V

3. In a voice operated circuit, a push-pull space discharge circuitnormally biased against transmission, means to impress. speech waves onthe input of said push-pull circuit, a three-element space dischargedevice coupled to the output of said push-pull circuit and having alarge resistance in its grid circuit, a rectifier connected to theoutput of said three-element device, normally biased against operation,the bias on said push-pull.

stage and that on the rectifier and the grid resistance of saidthree-element device all being proportionedto prevent production ofrectifier current in response to input waves below a certain minimumlevel and to produce saturation current in the rectifier in response toinput waves exceeding. said minimum level by a small fraction.

4. In a two-way voice operated system, an amplifier rectifier circuitfor controlling transmission in both directions in response to impressedspeech, said circuit comprising a push-pull space discharge tube stagenormally biased to the zero space current level, V

and means operating in response to waves from the opposite direction forincreasing said bias, said push-pull stage working into amplifierrectifier stages with steeply rising characteristics reaching saturationat input levels slightly in excess of initial operate level. I

In witness whereof, I hereunto subscribe my name this 29th day of May,1930.

BJORN G. BJORNSON.

